This application claims the priority of German patent document 10 2004 005 793.1, filed Feb. 6, 2004, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a control unit for a transportion device having a processing unit, such as programmable logic or a microcomputer, that is supplied with power by means of a first supply voltage and has a signal converter for converting analog signals to digital signals. The signal converter includes an analog converter portion for generating a modified signal from the analog signal at the signal converter input, and a digital converter portion for generating a digital signal from the modified signal. The analog converter portion includes a signal integration stage, whose output signals are fed to a signal amplitude comparator, and the digital converter portion includes a scanning stage, to whose output the analog-to-digital-converted digital signal is applied.
Nowadays, control units in transportation devices (such as motor vehicles, utility vehicles and airplanes) often carry out control tasks by reading and processing sensor signals, and controlling actuators (such as electric motors or air bag triggering units) based on their control signals. The sensors frequently supply an analog measuring signal which is converted to a digital signal by an analog-to-digital converter, so that the microcomputer of the control unit can process the digital signal to generate control signals. In conventional control units, analog-to-digital converters for this purpose are provided separately with respect to the microcomputer or a programmable logic of the control unit.
Conventional control units for transport devices have microcomputers or a programmable logic that include, among other items, functional blocks of the central computer core, program and data memories, timer units, input/output interfaces and serial interfaces. Today's microcomputers, such as microprocessors or microcontrollers, are normally operated by means of a 5 V supply voltage. In order to achieve a higher complexity or clock frequency, the structures on the semiconductor chips must become increasingly smaller, which in turn decreases the distances, particularly the thickness of the insulation layers, between semiconductor structures that operate with different voltage potentials. Therefore, when the semiconductor material is the same, in smaller structures the supply voltage must also be reduced to avoid discharges through the insulation layers, and thus the destruction of the semiconductor. The supply voltage of the microcomputers is therefore reduced to below 5 V.
However, as a result, when the analog-to-digital signal converter is supplied with the lower supply voltage, the signal-to-noise ratio on the analog side of the signal converter becomes very small. For example, if the peripheral voltage supply is reduced to 3.3 V or 2.5 V, the signal-to-noise ratio and the signal level swing of the analog signals falls significantly; and the sensors with a 5 V supply voltage (which are common in transport devices) cannot be reliably detected by the microcomputer without additional signal matching.
To solve this problem, it has been attempted to supply an analog-to-digital signal converter provided independently of the microcomputer of the control unit with 5 V, while the microcomputer or the alternative programmable logic of the control unit is controlled by means of a lower supply voltage. This results in higher costs for the additional voltage supply for the analog-to-digital signal converter. It should be taken into account in this case that the supply voltage should only be subjected to low voltage fluctuations so that the digital signals can finally be processed in the microcomputer. If greater voltage fluctuations or voltage differences occur at the voltage levels between the signal converter and the microcomputer, falsifications of the computing results occur during the processing of the digital signals in the microcomputer.
European Patent Document EP 1 300 951 A1 discloses a so-called delta-sigma signal converter which is divided into an analog and a digital converter part. The analog converter part has an integrator, a buffer and, connected thereto, a digital flip-flop from whose inverting output another storage element is fed back to the input of the integrator. The signal is scanned by the flip-flop which operates at very high scanning frequencies. To avoid problems with electromagnetic compatibility, the flip-flop is integrated in the digital converter part, preferably on a semiconductor chip.
One object of the present invention is to provide a control unit with a programmable logic or a microcomputer with an improved signal converter so that, while the supply voltage for the semiconductor chip of the microcomputer or of the programmable logic is reduced, high signal separation is possible at the analog signal levels of the analog-to-digital converter.
This and other objects and advantages are achieved by the control unit according to the invention, in which the digital converter portion is implemented by configurable logic circuits provided on the chip of the programmable logic or of the microcomputer, while the analog converter portion is provided by components outside the programmable log or the microcomputer. The analog converter portion is supplied with voltage by a second supply voltage that deviates from the first supply voltage.
The control unit is preferably suitable for motor vehicles and utility vehicles for controlling assemblies, the engine, the clutch or the starter generator of the transport device, for example. For this purpose, sensors may be provided at the transmission, the brake or at the chassis, which transmit analog sensor data to the control unit. The control unit has either a microcomputer, such as a microcontroller or microprocessor, or a programmable logic, such as a field programmable gate array (FPGA). Because of the very high clock frequencies, the microcomputer or the programmable logic are controlled by a lower supply voltage than the peripheral components outside the microcomputer or the programmable logic.
For example, the computer core may be supplied with a voltage of 1 to 4 V, while the peripheral circuits of the microcomputer and external logic components are provided with a 5 V voltage supply. By dividing the signal converter into a digital converter portion and an analog converter portion, the analog converter portion being supplied with a higher supply voltage, signal levels which are as large as possible are created on the analog side, so that a larger signal-to-interference ratio becomes possible in the case of these signals. As a result, serviceable signals are still created even in the event of a high-interference vehicle environment, permitting an interference-free control operation by means of the control unit.
The present invention has the advantage that the control unit completely eliminates the need for a discrete analog-to-digital signal converter or a conventional analog-to-digital signal converter which can be integrated in the microcontroller. The digital converter portion of the signal converter according to the invention is assigned to the microcomputer or to the programmable logic. That is, the circuit becomes a component of the configurable or programmable circuit of the respective input/output pins of the microcomputer or of the programmable logic. The analog converter portion with the integrator is not integrated in the microcomputer on the programmable logic but, depending on the requirements, has a discrete construction or is constructed as an individual circuit outside the microcomputer. However, multi-channel analog-to-digital signal converters can also be constructed in that several analog converter portions are connected in parallel and in each case interact with the pertaining digital converter portion on the microcomputer.
The external analog converter portion of the transport device control unit has a signal adder on its input, which adds the analog signal to be converted and a feedback signal from the digital converter part. As a result, the control unit constructed without a separate analog-to-digital signal converter has almost no analog circuit parts. Only a voltage regulator and special sensor interfaces are required.
The digital converter portion integrated in the microcomputer or the programmable logic preferably has counters, registers, clock multipliers and filters. By virtue of the special digital circuit parts, such as counters, registers, clock multipliers or filters, which already exist in microcomputers or programmable logics, the analog-to-digital signal conversion provided according to the invention can be carried out largely without stressing the CPU of the microcomputer. The special circuit parts, of which several are usually present, are preferably configured or programmed for the digital converter portion according to the invention. As a result, it also becomes possible to define freely the number of channels of the signal converter by means of software or external additional analog wiring. Unused channels will then be available after a corresponding configuration, for example, for the frequency or period length measurement or for generating pulse duration modulated signals.
In the signal converter according to the invention, a feedback signal is preferably provided from the output of the scanning stage, and is, for example, digital-to-analog-converted. Such a feedback signal is then fed to the adder at the input of the signal converter. The digital converter portion has a digital filter which processes the digital signals at the output of the scanning stage. The digital signals with the high scanning frequency can also be converted simultaneously into parallel signals, so that, for example, a parallel 10 bit signal can be created at the output of the signal converter.
Preferably, the first supply voltage for the programmable logic or the microcomputer is lower than 5 V, and the second supply voltage is greater than the first supply voltage. (The first supply voltage can, for example, be in the range of from 2 to 5 V, while the supply voltage of the analog converter part is at 5 V.) As a result, the chips can be miniaturized further for the microcomputer or the programmable logic, and the reduced first supply voltage permits an increased clock frequency of the microcomputer. Supply voltages of the digital computer core can then be implemented, for example, at 2.5 V or 1.8 V or 1.1 V. As a result of the second supply voltage at an increased voltage level, the signal-to-noise ratio and the signal level swing of the analog signals is significantly lowered, and the control signals of the microcomputer are less distorted by electromagnetic compatibility interferences. A portion of the digital converter part is wired as a timed storage element. A flip-flop can, for example, be used as a timed storage element. On the input side, the flip-flop is connected with the output signal of a comparator, so that, during each clocking, the flip-flop scans the comparator output signal and brakes it into individual pulses.
The signal of the flip-flop, which is quantified in this manner, is checked for digital signal changes and the number of required signal pulses for the signal level change is also counted. When an integrator is provided (for example, in front of the comparator), it is detected on the basis of the required clock pulses to the signal change at the output of the flip-flop which analog voltage level is applied to the input of the integrator. The corresponding digital signal will then in each case be present at the output of the digital filter connected on the output side. In this case, a corresponding signal coding can also take place here, so that the microcomputer can process the digital signal corresponding to its customary binary code. The digital filter is preferably implemented on the chip of the programmable logic or of the microcomputer.
The control unit according to the invention can be constructed with a separate analog-to-digital signal converter, which is programmed or configured by means of the circuit parts already existing on the microcomputer (such as counters, coding elements, filter components and logic circuits). As a result, the control unit largely requires no additional analog circuit parts which must be connected with the microcomputer via interfaces. A significantly higher integration or a further miniaturization on a single chip of the microcomputer or of the programmable logic therefore becomes possible; sensor signals are transmitted in a digital form from the sensor to the microcomputer. For this purpose, for the signal processing, the interface component present in the microcomputer or the programmable logic is used to convert the digital signals to the digital processing code of the control unit.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.